Abstract: The surface quality of nonoriented silicon steel is one of the important indicators of the product. During the production of a nonoriented silicon steel, the black spot defects appeared on the steel surface had a great impact on the stability of the production line and the product yield. Through macro observation and scanning electron microscopy (SEM), energy spectrum analysis, onsite simulation experiments, etc., the causes of black spots were studied. The results showed that the direct cause of the black spots was related to the "splash" of the coating liquid, and the occurrence of the defects was related to the operating state of the coating machine and the coating roller.

Key words: nonoriented silicon steel, black spot defect, coating, chromate coating, insulating coating